Bacteria in the genus streptococcus are a major cause of disease in man and some of his domestic animals. The primary treatment for these infections is therapeutic antibiotics. This use of antibiotics has lead to an increasing incidence of drug resistance among streptococci. The study of drug resistance in all bacterial systems coincides with the study of extrachromosomal genetic elements (plasmids) which most often mediate this drug resistance. In this regard we will undertake to define drug resistance in a selected group of strains in terms of cross resistance patterns, type of resistance and mechanism of resistance. The plasmids from these strains will be analyzed on the basis of molecular weight. Other techniques which will be employed include hybridizations as an indication of the relatedness of plasmids isolated from a number of different streptoccoci. Individual plasmids can be studied using equilibrium banding of DNA, agarose gel electrophoresis, and electron microscopy. Plasmid transmissibility will be measured from mixed culture experiments. Translocation of genetic elements and mobilization of chromosomal DNA are two areas of gene transfer we hope to explore more thoroughly in streptococcus with the use of plasmid mutants. The goal is to study the molecular biology and interactions of plasmids and evolution of plasmids using streptococcus as a system of study.